Geomagnetic effects on atmospheric Cerenkov images

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary -rays of energy ~300 GeV up to 10 TeV and to discriminate these from cascades due to hadrons using the Cerenkov images. The geomagnetic field affects the development of showers and is shown to diffuse and distort the images. When the component of the field normal to the shower axis is sufficiently large (>0.4 G) the performance of -ray telescopes may be affected, although corrections should be possible.